>>a creature that lived out its existence in a few microseconds might appear to us as a mere glitch in, say, an electric field,

From Wiki

Life is a condition that distinguishes organisms from non-living objects, such as non-life, and dead organisms, being manifested by growth through metabolism and reproduction. Some living things can communicate and many can adapt to their environment through changes originating internally. A physical characteristic of life is that it feeds on negative entropy.[1][2] In more detail, according to physicists such as John Bernal, Erwin Schrödinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena which are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form (see: entropy and life)
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Could such a creature feed on negative entropy? From the way you describe it, it is negative entropy. What about Metabolism? Reproduction? Wouldn't those things be detectable?

What would a gas cloud in space metabolize? As an uncontained gas cloud, its thermal energy would cause it to disburse. The more energy the faster the molecules would spread apart. By nature it would not be able to feed on negative entropy. So if a spaceship came upon a gas cloud which has some force acting upon it or within it which was allowing it to ignore Boyles Law, it might not be immediately recognizable as life but it would certainly be weird enough to be studied until Mr. Spock figured out why it was defying basic physical laws.

I was thinking about this before I went to sleep last night. I need to refine my statement. It would be very difficult to detect life in habitats that are highly inhospitable, the surface of a star, the magma of a planet. So I will say that if we can thoroughly observe it, we can determine if it is alive.